Electromechanical wheel brake device

ABSTRACT

An electromechanical wheel brake device has a helical gear for converting the rotating motion of an electric motor into a translating motion of a brake piston in order to press a brake pad against a brake disc in an advancing stroke or in order to release the brake pad in a restoring stroke. In addition, a clutch is provided, which operatively disengages a part of the helical gear from the electric motor should a permissible restoring stroke be exceeded. This prevents a mechanical failure or damage to the wheel brake device in the event of such a malfunction. The electromechanical wheel brake device can be used in motor vehicles such as cars.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 00/04147, filedon Nov. 23, 2000.

BACKGROUND OF THE INVENTION RECEIVED

1. Field of the Invention

The invention relates to an electromechanical wheel brake device for amotor vehicle, including a helical gear driven by an electric motor forapplying and releasing the brakes.

2. Description of the Prior Art

A wheel brake device is already known (DE 197 50 273 A1), in which athreaded spindle, which is part of a planetary roller screw drive andcan be moved in the longitudinal direction by a nut driven to rotate byan electric motor, is used to press a brake pad against a brake disc.The threaded spindle is comprised of two parts that axially interlock ina positively engaging manner. During normal operation of the wheel brakedevice, an inner part of the threaded spindle is kept axially androtationally stationary by an electromagnetically actuat d clutch; anouter part is guided on the inner part in a longitudinally mobilefashion. To avoid damage to the wheel brake device in the event of anincorrect continuous supply of power to the electric motor in therestoring stroke of the outer threaded spindle part, the clutch can alsobe mechanically switched by this part of the threaded spindle. As aresult, the threaded spindle can rotate freely and is operativelydisengaged from the electric motor.

SUMMARY OF THE INVENTION

The electromechanical wheel brake device according to the invention hasthe advantage over the prior art that the clutch for disengaging theelectric motor from the threaded spindle is comprised of fewercomponents than the known embodiment. This reduces both the weight andthe required installation space of the wheel brake device. The reducednumber of components also improves the operational safety of the wheelbrake device.

Advantageous modifications and improvements of the electromechanicalwheel brake device are disclosed.

One embodiment of the electromechanical wheel brake device allows theclutch to be engaged by simply reversing the rotation direction of theelectric motor.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is described herein below, withreference to the drawings, in which:

FIG. 1 shows a longitudinal section through an electromechanical wheelbrake device with a clutch in a threaded spindle and

FIG. 2 shows an enlarged detail of FIG. 1 with a clutch released fromthe threaded spindle.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An electromechanical wheel brake device 10 for motor vehicles shown inthe drawings is embodied as a disc brake. It has a floating caliper 11,in which two brake pads 12 are mounted one on either side of a brakedisc 13, which functions as a rotating friction element. To press thebrake pads 12 against the brake disc 13 and to release the brake padsfrom the brake disc, a longitudinally mobile brake piston 15 is disposedin the housing 14, which is connected to the floating caliper 11. Thehousing 14 also contains a helical gear 16 for displacing the brakepiston 15, a reduction gear 17 connected to the helical gear 16, and anelectric motor 18.

The electric motor 18, not shown in detail, has a rotor 21, which isnonrotatably connected to an input member 22 of the reduction gear 17,which is embodied as a planetary gear. The reduction gear 17 has anoutput member 23 for the torque transmitting engagement with a threadedspindle 24 of the helical gear 16, which is embodied as a ball screw.

The threaded spindle 24 is comprised of two parts 27 and 28, whichinterlock by means of positive engagement. The threaded spindle part 27disposed oriented toward the reduction gear 17 is supported in thehousing 14 of the wheel brake device 10 by an axial bearing 29 so thatit can rotate, but cannot move axially. A force sensor 30 for detectingthe brake force applied to the brake disc 13 by the brake pads 12 isdisposed between the housing 14 and the axial bearing 29 of the threadedspindle part 27, which is nonrotatably connected to the output member 23of the reduction gear 17.

The threaded spindle part 27 is equipped with a stepped journal 33 onthe side oriented away from the output member 23. The threaded spindlepart 28, which extends inside the brake piston 15, is supported on thisjournal 33. A nut 34 is associated with this threaded spindle part 28and is connected to the brake piston 15 in an axially fixed, nonrotatingfashion. A restoring stroke limiting stop 35 of the housing 14 of thewheel brake device 10 is associated with the brake piston 15 on its sideoriented away from the brake disc 13. In actual use, the brake piston 15assumes a position spaced apart from the stop 35; the distance of thisspacing depends on the wear on the brake pads 12 and the brake disc 13as well as the clearance between the brake pads and the brake disc.

The above-mentioned positive engagement between the two parts 27 and 28of the threaded spindle 24 is produced by a clutch 38, which can beembodied as a denture clutch or claw clutch. The clutch is embodiedalong the circumference of the journal 33 and/or at the end of the twoparts 27 and 28 of the threaded spindle 24. In the position shown inFIG. 1, the threaded spindle part 28 guided on the journal 33 isnonrotatably connected to the threaded spindle part 27 by means of theengaged clutch 38.

A connection rod 41, which is shaped as a fillister head screw, passesthrough the center of the two threaded spindle parts 27 and 28 and isscrewed into the output member 23 of the reduction gear 17. Two washers42 with a prestressed compression spring 43 between them are disposed atthe head of the axially stationary connection rod 41. The compressionspring 43 exerts spring force on the threaded spindle part 28 in thedirection of the threaded spindle part 27. The clutch 38 can bedisengaged by overcoming the spring force.

The electromechanical wheel brake device 10 functions as follows:

The electric motor 18 is supplied with power to actuate the wheel brakedevice 10. The rotating motion of the rotor 21 is transmitted to thethreaded spindle 24 of the helical gear 16 by means of the reductiongear 17. The helical gear 16 converts the rotating motion into atranslating motion of the brake piston 15. The brake piston 15 pressesthe two brake pads 12 against the brake disc 13 in a known fashion.

To release the wheel brake device 10, the electric motor 18 is suppliedwith power so that it reverses its rotation direction. The brake piston15, which is guided back into the housing 14, lifts the brake pads 12off of the brake disc 13. During proper operation of the wheel brakedevice 10, the brake piston 15 does not reach the stop 35 of the housing14.

However, in the event that the power supply to electric motor 18 remainsturned on due to a malfunction, then the brake piston 15 strikes againstthe stop 35. Consequently, the continuously propelled threaded spindlepart 28 is screwed into the axially fixed, nonrotatable nut 34 in thedirection of the brake disc 13. The longitudinal movement of thethreaded spindle part 28 on the journal 33 of the axially fixed threadedspindle part 27, which movement occurs counter to the force ofcompression spring 43, causes the clutch 38 to disengage after a limiteddistance. This position is shown in FIG. 2. The lack of positiveengagement between the two parts 27 and 28 of the threaded spindle 24releases the threaded spindle part 28, which is disposed on the side ofthe nut, from the electric motor drive, thus preventing overload anddestruction of the wheel brake device 10.

Upon elimination of the electric malfunction, the electric motor 18 isoperated to actuate the brake device; this resets the threaded spindlepart 28 due to the frictional engagement of the connection rod 41 andthe threaded spindle part 28 and restores the positive engagement withthe threaded spindle part 27.

The foregoing relates to the preferred exemplary embodiments of theinvention, it being understood that other variants and embodiments arepossible within the spirit and scope of the invention, the latter beingdefined by the appended claims.

1. In a electromechanical wheel brake device (10) for a motor vehiclewith an electric motor (18) for actuating and releasing the wheel brakedevice (10), with a helical gear (16) converting the rotating motion ofthe electric motor (18) into a translating motion in order to press abrake pad (12) against a brake disc (13) and release it from the brakedisc, the helical gear (16) having a nut (34) and a threaded spindle(24), the threaded spindle being comprised of a first part (27) and asecond part (28) that interlock by means of positive engagement, with aclutch (38), which can be at least indirectly actuated in the event of amalfunction-induced release of the brake pad (12) from brake disc (13)and which operatively disengages the electric motor (18) from the secondpart (28) of the threaded spindle (24), the improvement wherein: theelectric motor (18) engages the first part (27) of the threaded spindle(24), the second part (28) of the threaded spindle (24) engages with thenut (34) of the helical gear (16), the nut (34) of the helical gear (16)is moveable in the longitudinal direction along the threaded spindle(24) and is at least indirectly associated with a stop (35), whichlimits a restoring stroke, and the first and second parts (27, 28) ofthe threaded spindle (24) are disengaged by means of the clutch (38)when the nut (34) of the helical gear (16) engages at least indirectlywith the stop (35).
 2. The electromechanical wheel brake deviceaccording to claim 1 wherein the first part (27) of the threaded spindle(24) is supported in an axially stationary manner in a housing (14) ofthe wheel brake device (10), while the second part (28) of the threadedspindle (24), which engages with the nut (34) of the helical gear (16),can be operatively disengaged from the first part (27) in an axiallymoveable fashion counter to a spring force.
 3. The electromechanicalwheel brake device according to claim 2 further comprising an axiallyfixed connection rod (41) passing through the center of the second part(28) of the threaded spindle (24) and having a compression spring (43),which loads the second part (28) with a spring force oriented toward thefirst part (27) of the threaded spindle (24).
 4. The electromechanicalwheel brake device according to claim 1 wherein the second part (28) ofthe threaded spindle (24), on its side oriented toward the clutch, isguided in a longitudinally mobile fashion on a journal (33) of the firstpart (27) of the threaded spindle (24).
 5. The electromechanical wheelbrake device according to claim 2 wherein the second part (28) of thethreaded spindle (24), on its side oriented toward the clutch, is guidedin a longitudinally mobile fashion on a journal (33) of the first part(27) of the threaded spindle (24).
 6. The electromechanical wheel brakedevice according to claim 4 wherein the clutch (38) is embodied alongthe circumference of the journal (33) and/or at the end of the first andsecond parts (27, 28) of the threaded spindle (24).
 7. Theelectromechanical wheel brake device according to claim 5 wherein theclutch (38) is embodied along the circumference of the journal (33)and/or at the end of the first and second parts (27, 28) of the threadedspindle (24).